Food production on land areas experiences extreme environmental conditions in the above-ground environment. Environmental conditions include variation in air temperature, wind speed, light levels, relative humidity and available nutrients and water. Methods for protecting plants from extreme environmental conditions are desired since they would increase the amount and stability of food production.
While foliage reflectance is recognized as a means of moderating environmental extremes, such techniques result in reduced photosynthesis. Generally speaking, foliage sprays cause a long-term reduction in the rate of CO.sub.2 uptake (photosynthesis) and enhance leaf senescence. Thus, although plant survival may increase with a foliar application of a reflective material, decreased transpiration and decreased photosynthesis undesirably occurs. Photosynthesis and transpiration in plants are positively linked in that a decrease in transpiration generally leads to a decrease in photosynthesis.
For example, reflective coatings are applied to the surfaces of fruits and vegetables to reduce excessive heat and light (including ultraviolet (UV) light and infrared (IR) light) at the fruit surface in an attempt to prevent a condition known as "sunburn". While the precise cause of sunburn is unknown, sunburn is a disorder that appears as a darkened area on the surface of fruits and vegetables. Beneath the sunburned area, the fruit tissue is damaged and likely to develop disease symptoms. The combination of off-color and increased disease susceptibility makes the fruit unmarketable. The strategy of applying a reflectant treatment is to reduce the temperature of the fruit by reflecting heat or by blocking light including UV and IR light.
Reducing fruit temperature by spraying the fruit with water, evaporative cooling, reduces other apple physiological disorders such as watercore, corking and bitterpit. Evaporative cooling is also used to reduce sunburn. The application of evaporative cooling water increases yield by increasing available water to the plant and increasing photosynthesis. However, the negative aspects of high costs, high maintenance, and the possibility of being subjected to water restrictions are associated with evaporative cooling.
In perennial crop production such as tree fruit, flower buds for the subsequent year are initiated while fruit are developing for the current growing season. In practice, a plant may or may not produce flower buds for the subsequent year. One of the many biochemical cues to develop flower buds is the rate of photosynthesis and the availability of photosynthetically derived carbohydrates for flower bud development.
The availability of carbohydrates is limited by the photosynthetic capacity of the plant and the pool of carbohydrates is partitioned between the competing carbohydrate needs of the woody tissue, leaf tissue, developing flower buds and developing fruit. If photosynthesis is limited by excessive heat or water stress during the flower bud initiation period, flower bud initiation is reduced and fewer flowers are produced the following season. Reduced flower number results in reduced fruit number. In the subsequent year, the tree has a reduced number of fruit and it develops excessive numbers of flower buds because it lacks the competing developing fruit when flower buds are initiated. The alternating production of large and small numbers of fruit is an undesirable condition known as "alternate bearing".
A related problem to alternate bearing is called "excessive fruit drop". Normal fruit drop occurs when, simultaneously, the fruit is developing, tree growth is occurring, and flower buds are being initiated. Photosynthetically derived carbohydrates become limiting to all the growing tissues at this time in the growing season and the plant aborts the developing fruit, and limits the initiation of flower buds. When environmental conditions deleteriously effects or diminishes photosynthesis, fruit drop is excessive. Furthermore, UV and IR radiation may have damaging effects on plant tissue. UV and/or excessive IR radiation damage the photosynthetic mechanism of plants and reduce plant productivity.
Various materials are used to 1) reduce winter damage; 2) delay the onset of bloom in order to avoid spring frosts; and 3) prevent UV radiation damage. However, there are problems associated with applying various materials to fruits. For example, while various materials may address one or more of the three above mentioned concerns, these materials tend to diminish photosynthesis. Another problem relates to the difficulty of providing inert and low toxicity materials for use with plants. Yet another problem is easily and/or thoroughly cleaning or rinsing materials from fruits.